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Weird result to IAC/Throttle Body cleaning

2219 Views 8 Replies 7 Participants Last post by  mellowflyer
My 1999 Mustang GT had been idling rough, but when I turned the A/C on the idle would be smooth.


So I figured I will clean the IAC and I might as well clean the throttle body at the same time. Went out, bought some throttle body cleaner and did the easy job after watching a couple of videos/reading some guides.


I turn on my car and let it run without the A/C on for awhile and am very happy as the car is idling much better! Then I turn the A/C on and the car idles rough... Just like it did before, when I had the A/C off.


It seems as if the cleaning just switched rough idle from idling rough without the A/C on to it idling rough with the A/C on... Any thoughts?


I did spray throttle body cleaner into the actual engine hole where the IAC is placed back on, don't know if that was a bad move on my part.
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Not sure about your Mustang, but likely cleaning the TB was a good thing. The IAC (idle air control) is something else. I cleaned my IAC on the old Dodge truck regularly, and it was just to wipe off the carbon with a rag, and a dry q-tip into the well. I never sprayed it with anything nor used any cleaner. I'm guessing that plain and simple 91% alcohol might have ill effect. But TB or carb cleaner might. Those sensors can be rather sensitive (no pun intended).
I know very little about the Mustangs let alone my specific model (yet). On my former Dodge truck, I could actually remove the IAC from the TB.
Trouble shooting.......have you driven your Mustang since the cleaning, or just started and let it idle?
I know that the A/C compressor cycling will down the RPMs on mine at a stop and in drive to where I can feel it just for an instant.
Maybe you could try the battery disconnect ordeal that's so often spoken about to see if that changes anything.
At some point I'll be wanting to clean my TB properly as well. I know all too well that sometimes you can open a can of worms.
Hopefully you'll get some good input on this ordeal. More than likely it's happened to someone else. I have a 2011 V6.
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I personally think you just need to replace your IAC. Motorcraft or nothing. Cleanings an IAC is really only temporary at best.

Any DTCs the computer is throwing?
LOL I did the exact same thing to my car about 2 months ago and ended up with the same results as you :heha:, My problem was the car was low on refrigerant , If you can get the a/c pressure's check so you can avoid further damege to the a/c .
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LOL I did the exact same thing to my car about 2 months ago and ended up with the same results as you :heha:, My problem was the car was low on refrigerant , If you can get the a/c pressure's check so you can avoid further damege to the a/c .
Looks like I am going to get my pressure checked, thanks!
I will also try to disconnect the battery and see if that changes anything. I have not driven my mustang since the day I cleaned everything. I cleaned everything right before I took a rental car to Kentucky, but I will know tomorrow what the update is. After getting my A/C pressure checked I will look into getting a new IAC. The car isn't throwing any codes. Thanks for the input, I will post a little update soon.
As a reminder. It takes time for the PCM to re-LEARN new iac/idle trim values after a battery disconnect. Sooooooooooooooooooo disconnecting the battery has the effect of restarting the learning process.

Disconnecting the battery with no repair is likely only to slow the re-learning process. However, if repairs have been made it most certainly is a good idea to disconnect the battery to allow re-learning to occur from the repaired "base" line.

Check out the following recent thread regarding HOW the PCM works with the IAC and the AC.

http://www.allfordmustangs.com/foru...rned-car-bucks-high-idles-inconsistently.html
I sprayed mine down with carb cleaner and it worked fine? I'd go ahead and check for leaky hoses or anything else that could cause it...
My 97 was having problems idling. I cleaned the IAC and it had little to no effect. Replacing the IAC fixed it 100%.
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